1. Field of the Invention
The present invention relates to an optical system for projection and a projection-type display apparatus. Particularly, the present invention relates to an optical system for projection that has taken temperature compensation into consideration and a projection-type display apparatus on which the optical system for projection is mounted.
2. Description of the Related Art
Conventionally, projection-type display apparatuses, which magnify and project an image displayed on a light valve, were used in presentation and the like. As the light valve, a transmission-type liquid crystal display device, a reflection-type liquid crystal display device, a DMD (Digital Micromirror Device: Registered Trademark) and the like are known. Meanwhile, a high output power light source is often used in a projection-type display apparatus. Therefore, temperature changes in the optical system. In recent years, the level of the definition of a projection-type display apparatus became higher because of a progress in the light valve and the like, and an out-of-focus condition caused by a change in temperature in the optical system became more noticeable. Further, as a higher definition became requested, a material with a large Abbe number (for example, a material with an Abbe number of 75 or higher) became often used to reduce chromatic aberrations, and that also increased the degree of the out-of-focus condition caused by the change in temperature.
As related techniques about optical systems for projection with respect to correction of an out-of-focus condition caused by a change in temperature, techniques disclosed, for example, in Japanese Unexamined Patent Publication No. 2008-046259 (Patent Document 1), Japanese Unexamined Patent Publication No. 2011-022498 (Patent Document 2) and Japanese Unexamined Patent Publication No. 2006-048013 (Patent Document 3) are known. Patent Document 1 discloses a technique for offsetting a shift in a focal position caused by a change in temperature in a projection-type zoom lens by arranging anomalous dispersion glass with an Abbe number of 70 or higher at appropriate positions by using the anomalous dispersion glass in a positive lens and a negative lens, and by making each of the positive lens and the negative lens constitute a cemented lens. Patent Document 2 discloses a projection lens apparatus that offsets a shift in a focal position caused by a change in temperature of anomalous dispersion lens by the amount of movement of the anomalous dispersion lens caused by a change in temperature of a lens barrel in which a lens group including the anomalous dispersion glass is arranged. Patent Document 3 discloses a technique for correcting a change in a distance between an object and an image caused by a change in temperature. The change in the distance is corrected by supporting at least a part of lenses in a light-source-side positive lens group by plural members having different linear expansion coefficients from each other, and by moving the lenses in the direction of an optical axis by a difference in expansion or contraction of the plural members caused by a change in temperature.